Apheresis blood processing plays an important role in a large number of therapeutic procedures. In these procedures, blood is withdrawn from a patient undergoing therapy, separated, and a selected fraction is collected while the remainder is returned to the patient. For example, a patient may undergo leukapheresis prior to radiation therapy, whereby the white blood cell component of his blood is separated, collected and stored to avoid exposure to radiation.
Both conventional blood collection and apheresis systems typically employ differential centrifugation methods for separating blood into its various blood components. In differential centrifugation, blood is circulated through a sterile blood processing vessel which is rotated at high rotational speeds about a central rotation axis. Rotation of the blood processing vessel creates a centrifugal force directed along rotating axes of separation, oriented perpendicular to the central rotation axis of the centrifuge. The centrifugal force generated upon rotation separates particles suspended in the blood sample into discrete fractions having different densities. Specifically, a blood sample separates into discrete phases corresponding to a higher density fraction comprising red blood cells and a lower density fraction comprising plasma. In addition, an intermediate density fraction comprising platelets and leukocytes forms an interface layer between the red blood cells and the plasma. A number of complementary separation techniques based on filtration, elutriation in a cell separation chamber and affinity-based techniques have been developed to achieve higher purities needed for use of blood components as therapeutic agents.
Embodiments of the present invention have been made in light of these and other considerations. However, the relatively specific problems discussed above do not limit the applicability of the embodiments of the present invention.